1. Field of the Invention
The present invention pertains to switches for electrical appliances and in particular to operating mechanisms for such switches having the ability to lock in a constant energized mode.
2. Description of the Related Art
Electrical appliances, especially appliances having electric motors have been provided with push buttons to switch the motor on and off as desired. Electric power tools, for example, are sometimes used for long periods of time and it is desirable to provide an electric switch which need not be constantly pressed to switch the motor on. Accordingly, a variety of arrangements have been provided to lock a push button electrical switch in an operating position. Such arrangements are alternatives to so-called "rocker" switches or "toggle" switches which incorporate mechanical mechanism having a bistable mode of operation.
Russian Patent No. 147,622 and Offenlegungsschrift No. 23 48 668 have switch operators with a window for receiving a stepped push button. The button can be operated so as to bring different stepped portions into engagement with the actuator window, thus providing different modes of operation. For example, the actuator window can be selectively held in a first position in which the electrical switch is turned on.
U.S. Letters Pat. No. 3,378,662 provides a trigger button having an internal saw tooth edge. A separate locking button has an enlarged free end which engages the teeth of the push button arrangement, thus locking the push button at a desired depressed condition. The locking button is spring-loaded so that, with increased pressure applied to the trigger button, the lock button will be released, thereby allowing the trigger button to move to an undepressed position. Thus, the trigger button can be moved to a number of depressed positions, corresponding to the number of teeth internal to the button mechanism.
U.S. Letters Pat. No. 3,309,484 provides a simpler locking mechanism for a trigger button which has an aperture formed in the button actuator. A trigger button is located along the path of travel of the trigger button, and is extendable into the path of the trigger button so as to be received in the trigger button aperture, thus locking the trigger button in a depressed position. Both the trigger button and the locking button are spring loaded to facilitate release of the trigger to an undepressed position. Locking arrangements which interfere or interlock with a trigger button are also disclosed in U.S. Letters Pat. Nos. 3,662,136; 3,869,591, and 3,953,696.
U.S. Letters Pat. No. 3,781,579 provides a sliding lock which interferes with the movement of a trigger button. The sliding lock operates an intermediate plunger member which in turn interferes with the trigger button, maintaining the button in a depressed position.
German Patent No. DTL 017151 discloses a locking electrical switch having a trigger button with a recess on one edge, and a slotted tail member for engaging the arm of a spring loaded electrical contact. The trigger button is spring loaded with a separate spring member. A crank arm is pivotally mounted in the switch mechanism, adjacent the trigger button and includes a pawl tooth to be received in the recess of the trigger button. The crank arm is spring biased to a position for engagement with the trigger button, using a separate spring member. A lock button is engageable with the crank arm to move the pawl tooth out of engagement with the trigger button, thus freeing the trigger button for movement to an undepressed position.
The above switch mechanisms are relatively complicated to fabricate and install in an electrical appliance. Further, when a molded housing is employed with the electrical appliance, the housing design is complicated as the number of switch components is increased, thus complicating the mold design and further adding to the cost of the appliance.
It is desirable to provide a push button lock having momentary operating positions in addition to a selectable locking arrangement for moving the switch between two or more stable operating positions. However, to be economically attractive to an appliance manufacturer, such arrangements should have fewer moving parts which are inexpensively formed using conventional materials. Double insulated tools, for example, are frequently made with molded plastic housings and it is advantageous to provide switch mechanisms having molded plastic parts. Further, it is desirable to provide a switch mechanism with moving parts which are less delicate, and which will provide reliable operation over the life of the electrical appliance.
Further, it is desirable in some situations to employ a commercially available electrical switch component such as a miniature switch having a hollow plastic housing and an actuator stub shaft protruding from a surface of the housing.